Method of optical correction for preprinting drawn articles



April 7 H. J. WOLBERT METHOD OF OPTICAL CORRECTION FOR PREPRINTING DRAWN ARTICLES Filed Oct. 6, 1964 FIG. 6

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IN VENTOR. Harris. Jay Wolbjert ATTORNEY United States Patent 3,314,329 METHOD OF OPTICAL CORRECTION FOR PREPRINTING DRAWN ARTICLES Harris Jay Wolbert, Prospect Heights, Ill., assignor to American Can Company, New York, N.Y., a corporation of New Jersey Filed Oct. 6, 1964, Ser. No. 401,863 Claims. (Cl. 88-24) This invention relates to a method for optically distorting a flat image or design so that such an image or design will appear to be correct and symmetrical when converted into a tubular configuration. More particularly, this invention relates to a method for photographically converting a normal, undistorted image into a precompensated, deliberately distorted annular image which can be imprinted upon a flat blank formed of metal, plastic or other similar material. When such a printed blank is drawn into a tubular configuration, the distorted annular image will appear in undistorted form upon the side walls of the tubular body.

In the manufacture of shallow-depth metallic containers, such as tuna fish cans, it is often the practiceto resort to a drawing operation wherein a flat circular blank of metal is reformed in a drawing die into a cupshaped configuration having a circular bottom wall and an integral upstanding tubular side wall. During such drawing operation, the portion of the blank forming the side wall is stretched and distorted in a predictable man- Due to the fact that side wall distortion does occur during a drawing operation, it has been recognized that a label or design cannot readily be preprinted onto a blank prior to a drawing operation since that label or design would become distorted as the blank is drawn. Oustomarily, such blanks were not, therefore, preprinted, but instead, the container formed from such a blank was labeled by (1) printing upon the side walls after the container was already drawn into a tubular form; (2) printing upon a fiat paper label and adhesively securing such a label to the finished container side wall; or (3) printing upon the fiat top or bottom of the container. Naturally, none of these printing techniques was particularly satisfactory, since technique (1) was slow and cumbersome, thus increasing the cost of manufacture of the containers; technique (2) presented a label which was easily torn or mangled during shipping, thus detracting from the appearance of the container; and technique (3) created a container in which the label could not be readily observed when the containers were stacked or nested.

It will, of course, be readily appreciated from the foregoing matter that the most satisfactory and inexpensive manner for preparing a label for a container is to preprint the blank from which the container is formed. Even though distortion of the side walls of a drawn can was recognized as a serious drawback to preprinting, there have, nevertheless, been attempts made in the past to preprint the can blanks prior to drawing. These attempts, however, have always taken the form of a handpainted artistic distortion produced by the use of grid work and reference points. Naturally, such a handpainted distortion is extremely slow and tedious to produce and, moreover, it is not always a completely accurate distortion. Additionally, such distortions were limited to crude patterns since the artist producing them was unable to accurately portray more complicated and detailed types of images.

With the foregoing in mind, it is, therefore, an object of the present invention to overcome the shortcomings associated with the prior art and to provide in their stead, an improved method of selective photographic image distortion.

3,314,329 Patented Apr. 18, 1967 Another object of the present invention is to provide a method for converting an undistorted normal image into an image which is distorted into an annular configuration.

Another object of the present invention is to provide a method for decorating the side wall of a drawn container with an undistorted image or label.

Another object of the present invention is to provide a method for preprinting a fiat container blank to-be used in a drawing operation for forming a tubular container having decorated or printed side walls.

Another object of the present invention is to provide a method of optically correcting an image into a precompensated distorted configuration and for imprinting that distorted image upon a blank to be subsequently drawn into a tubular container, with the imprinting to be effected in such a manner that the image appears in undistorted form upon the side walls of the finally drawn tubular container.

Another object of the present invention is to provide a method of photographic optical correction which is fast, accurate and inexpensive.

Numerous other objects and advantages of the present invention will become apparent from the following detailed description which, taken in conjunction with the annexed drawings, discloses a preferred embodiment thereof.

The foregoing objects are attained by providing a method wherein the design to finally appear on the side wall of a finished container is provided on a flat label. The design on the flat label is first photographed in such a manner as to produce an image of foreshortened height. This image is then wrapped around a mandrel having a periphery substantially equivalent to the length of the image. Then the mandrel, with the image wrapped thereon, is placed coaxially within a generally frustoconical mirror of predetermined dimensions and angle, and the image reflection upon the mirror is photographed. This second photographic step forms the image into a compensated annular configuration.

The annular image is then transferred to a printing plate by a suitable process such as photolithography. The printing plate is used to apply the annular image to flat container sheet stock which is subsequently blanked into a desired, e.g. circular, shape. On this circularly shaped blank, the outer periphery or margin contains the distorted annular image. The circular blank is finally introduced into a drawing die wherein it is converted into a finished tubular container. On the side walls of this container. the design appears in true and undistorted form.

Referring to the drawings:

FIG. 1 is a perspective view of a planar undistorted label being photographed at an angleto foreshorten the height thereof;

FIG. 2 is a perspective view of the foreshortened image produced by the photographic step of FIG. 1;

FIG. 3 is a side elevational view, partly in section, of the foreshortened image of FIG. 2 being wrapped about a mandrel disposed within a frusto-conical mirror, and of the reflected image within that mirror being photographed;

FIG. 4 is a top plan view of the photograph taken in FIG. 3 and showing the image converted into a complete ly distorted annular configuration;

FIG. 5 is a perspective view of the image of FIG. 4 being imprinted onto suitable sheets of containerstock;

FIG. 6 is a sectional side elevational view of a means for blanking a suitable container blank from the imprinted sheet of container stock; and

FIG. 7 is a sectional side elevational view of a means for drawing the container blank into a tubular configuration.

As a preferred or exemplary form of the present inven tion and as an illustrative means for depicting the novel series of steps carried out therein, reference is made to FIG. 1 wherein a label generally designated is shown spaced away from a suitable photographic means or camera generally designated 12.

The label 10 can be seen to be a generally flat or planar sheet having indicia 14 linearly imprinted on one surface thereof. The particular nature of the indicia or design 14 is variable in its content and, as aforesaid, forms the image which will finally appear, in its undistorted form, upon the side walls of a drawn tubular container. For ease of description of the ensuing steps herein, the label 10 is shown as having a height H and a length L, although it will be understood that the actual dimensions of any particular label can be varied, as desired.

In FIG. 1, the. label 10 is disposed at an angle to the lens 16 of the camera 12. The purpose of such an angular disposition is to permit a photograph to be taken in which the height of the label, and hence the height of the indicia 14 thereon, is neduced or foreshortened. To this end, one lengthwise edge of the label 10 is inclined further away from the camera lens 16 than is the other lengthwise edge, or, in other words, the label 10 is disposed at an angle X to an imaginary plane 18 which is parallel to the lens 16 of the camera 12.

FIG. 2 is a representation of the photograph taken in FIG. 1. As will be noted, the length L of the label has remained constant, but the height H has been somewhat reduced or foreshortened, thus reproportioning the height of the indicia 14 thereon. The purpose for such reproportioning of the height of the image or indicia is that, during a drawing operation, the metal that is drawn along the shank of the drawing punch is stretched or elongated, and naturally, the image thereon is likewise stretched or elongated in height. Consequently, the reproportioning step of FIG. 1 precompensates for such stretching to assure that the indicia will be the proper height after the drawing operation is completed. Instead of photographing the label at a predetermined angle as shown 'in FIG. 1, it is possible, if desired, to accomplish the reproportioning by utilizing a cylindrical lens having a concave or convex configuration.

()nce the reproportioning step has been completed, and the label converted to a foreshortened form such as shown in the photograph illustrated in FIG. 2, such a photograph is then wound about the exterior of a mandrel 20, as shown in FIG. 3. The circumference of the mandrel 20 corresponds to the length L of the label so that no space is left between the opposite ends of the photograph after winding upon the mandrel. The camera 12 is then disposed over the end of the mandrel 20 in such a manner that the lens 16 is centrally over the end of the mandrel. Thus, an imaginary axis 22 extends between the lens and the mandrel and forms the central axis of each, and the label 10 upon the mandrel is equally radially spaced from the axis 22.

A frusto-conical mirror 24, or a member having an internally mirrored surface, is disposed over the end of the mandrel 20 in such a manner that the indicia 14 on the label 10 is reflected upon the mirror surface. It will be noted that the opposed ends of the frusto-conical mirror 24 are open to permit the mandrel 20 to be freely introduced thereinto and removed therefrom. The larger of the mirror ends is disposed closest to the camera 12 while the smaller of its ends extends along the mandrel to at least the end edge of the label 10. In this manner, as will be seen in FIG. 3, the walls of the mirror 24 taper outwardly from the mandrel 20 and diverge as they extend toward the camera 12. The angle of divergence between the walls of the mirror 24 and the imaginary central axis 22 is identified as Y. The preferred value for the angle Y is 45 Once the camera 12 photographs the image appearing in the mirror 24, as shown in FIG. 3, the resulting print of such a photograph will appear in the form shown in FIG. 4. As can be seen, the print of FIG. 4 depicts an annulus whose outer limit 24a is formed by the photograph of the edge of the larger end of the mirror 24 and whose inner limit 20a is formed by the photograph of the end of the mandrel 20. Within the annulus, the indicia 14 has become completely distorted. It will be appreciated that by the steps shown in FIGS. 1 and 3, the label 10 is photographically converted from the planar linear undistorted image shown in FIG. 1 to the planar annular distorted image shown in FIG. 4.

The annular distorted image shown in FIG. 4 is then transferred onto a printing plate 26 by any suitable process such as photolithography, photoengraving, or the like. The printing plate 26 is then mounted upon a suitable printing roll 28, as shown in FIG. 5, and as flat sheets 30 of container stock are fed beneath the roll 28, the distorted annular image is imprinted thereon. The imprinted sheet 30 is then placed within a blanking die 32, as shown in FIG. 6, and a punch 34 is reciprocated to punch or blank out a suitable circular disc 36 which is to be drawn into the final container. It will, of course, be understood that in actual practice several printing plates 26 are mounted on a single elongated rel-1'28 so that a wide web 30 of container stock can beused, with several images being simultaneously imprinted thereon. Similarly, the blanking station is provided with a multiple series of aligned dies and punches to permit several discs 36 to be simultaneously blanked out of the stock. However, for ease of illustration, FIGS. 5 and 6 show only a single imprinting and blanking operation.

Once the disc 36 has been formed, it is placed within a drawing die 38, as shown in FIG. 7, and a drawing punch 40 is reciprocated downward to strike the disc 36 and to draw it Within the drawing die. In the actual drawing operation, the central portion of the disc 36 moves downward in contact with the end of the punch 40 and is not stretched. However, the outer margin of the disc is drawn between the walls, the die 38 and along the shank of the punch 40, thus stretching it. This stretching operation causes the distorted image or indicia to resume their true undistorted form on the straight side walls of the finally formed drawn tubular container 42.

The amount of side wall stretch, and hence the amount of distortion of the printing, can be calculated from the type of material used in the disc, the diameter of the disc, and the desired diameter, wall height and flash for the finally formed container 42. As an example, the disc for a tuna fish can is 6%" in diameter. This disc is to be drawn into a can having a bottom diameter of 3% two side walls having a total height of 3 with A" allotted for total flash. Since the bottom and the flash are not stretched at all during the drawing operation, the amount of material left to be stretched is 27 (the 6 /8" disc diameter minus the 3%," bottom diameter and minus the /4" total flash). Since walls are formed at each side of the bottom, there can really be considered to be two side walls, each to have a final height of 1 (one half of 3 alloted for the total side wall height). The material to be stretched to this 1 height is only 1 (one half of the 2 left available for stretching) prior to the drawing operation. Thus, during the drawing operation, the 1 4 is stretched to 1 for a total percentage stretch of 29%. In precompensating for this stretch, the image is properly distorted for a 29% stretch.

In some instances, the amount of stretch can be considerably greater than for the tuna fish can previously described. Thus, to form a conventional 208 X 208 can, the initial disc is only 5 /2" in diameter. Since the finally formed can is to have a bottom diameter of 2 /2" and tWO walls each 2 /2" high (or a total side wall height of 5") and since the central 2 /2" of the disc are not stretched during drawing, that means that the outer or maginal 3" on the disc must be stretched to 5" (the total side wall weight) for a total percentage stretch of 70%.

Although the foregoing matter has been concerned primarily with the formation of a cylindrical container, it should be understood that the principles of the present invention are equally applicable to oval containers, obround containers, conical containers, and other similarly shaped containers, and the term tubular as used herein is intended to comprehend all such shapes. Further, the area Within the distorted annular image may also be decorated by conventional means so that the finished, drawn container will be decorated on its flat or planar end as Well as its sides.

It is thought that the invention and many of its attendant advantages will be understood from the foregoing description and it Will be apparent that various changes may be made in the steps of the method described herein and in their order of accomplishment without departing from the spirit and scope'of the invention or sacrificing all of its material advantages, the form hereinbefore described being merely a preferred embodiment thereof.

I claim:

1. A method of optical correction for preprinting a container to be subsequently drawn into a tubular shape, said method comprising the steps of:

providing a label having a linear undistorted image thereon;

photographing said label so as to produce an image of foreshortened height;

wrapping the photograph of said foreshortened height image about a suitably sized mandrel;

disposing the mandrel coaxially within a generally frusto-conical mirror or predetermined size and angularity so that said foreshortened height image will be reflected into said mirror;

photographing the image reflected in said frustoconical mirror to produce an image having a selective distortion;

imprinting the selectively distorted image onto a blank and drawing at least a part of said blank into a tubular container wherein said selectively distorted image appears in undistorted form upon the side walls of said tubular container.

2. A method as defined in claim 1 wherein the angle between said mirror and said mandrel is substantially 45.

3. A method as defined in claim 1 wherein said mandrel is cylindrical and has a diameter substantially equivalent to the diameter of said tubular container.

4. A method of decorating the side Wall of a drawn tubular container with an undistorted image, said method comprising the steps of:

providing a planar label having the desired decoration imprinted thereon;

photographing said label at a predetermined angle to convert said decoration into an image of foreshortened width;

converting the photograph of said foreshortened width into a cylindrical configuration;

disposing said cylindrically converted photograph Within a frusto-conical mirror whereby said foreshortened width image will be angularly reflected in said mirror; photographing the image within said mirror to form a 6 completely distorted image of an annular configuration; reproducing said distorted annular image on a printing plate;

" cumference of said mandrel is substantially equal to the length of said photograph.

7. A method as defined in claim 4 wherein the angle between said mirror and said mandrel is substantially 45.

8. A method as defined in claim 4 wherein the step of imprinting the annular image on said sheet container stock includes the steps of:

mounting said printing plate on a rotatable roll means;

and

passing a planar sheet of container stock in contacting relation across the surface of said printing plate.

9. A method as defined in claim 8 wherein the drawing step includes first blanking from said sheet, a circular container blank and thereafter introducing said container blank into a drawing die which is operative to convert said blank into a tubular configuration.

10. A method of correction for preparing a blank to be subsequently drawn into a tubular shape comprising the steps of:

providing a label having a linear undistorted image thereon;

photographing said linear image so as to provide a reproduction of said linear image having a foreshortened height;

converting said reproduction into a cylindrical configuration;

arranging said cylindrically converted reproduction within view of a conical reflecting surface whereby said precompensated configuration will be reflected .in said conical surface; photographing said reflected configuration to form a distorted image of an annular configuration; reproducting said distorted annular image on a sheet of container stock; and

drawing at least part of said sheet container stock into a tubular container whereon the image appears in undistorted form upon the side Walls thereof.

References Cited by the Examiner UNITED STATES PATENTS 1/1963 Packard 8824 X 9/ 1964 Pettis 88-24 

1. A METHOD OF OPTICAL CORRECTION FOR PREPRINTING A CONTAINER TO BE SUBSEQUENTLY DRAWN INTO A TUBULAR SHAPE, SAID METHOD COMPRISING THE STEPS OF: PROVIDING A LABEL HAVING A LINEAR UNDISTORTED IMAGE THEREON; PHOTOGRAPHING SAID LABEL SO AS TO PRODUCE AN IMAGE OF FORESHORTENED HEIGHT; WRAPPING THE PHOTOGRAPH OF SAID FORESHORTENED HEIGHT IMAGE ABOUT A SUITABLY SIZED MANDREL; DISPOSING THE MANDREL COAXIALLY WITHIN A GENERALLY FRUSTO-CONICAL MIRROR OR PREDETERMINED SIZE AND ANGULARITY SO THAT SAID FORESHORTENED HEIGHT IMAGE WILL BE REFLECTED INTO SAID MIRROR; PHOTOGRAPHING THE IMAGE REFLECTED IN SAID FRUSTOCONICAL MIRROR TO PRODUCE AN IMAGE HAVING A SELECTIVE DISTORTION; IMPRINTING THE SELECTIVELY DISTORTED IMAGE ONTO A BLANK AND DRAWING AT LEAST A PART OF SAID BLANK INTO A TUBULAR CONTAINER WHEREIN SAID SELECTIVELY DISTORTED IMAGE APPEARS IN UNDISTORTED FORM UPON THE SIDE WALLS OF SAID TUBULAR CONTAINER. 